Gene, not sure I'm thinking right on this, because my AT&T router I believe is also the modem, where as you say yours are separate. Remember about resetting the router with the tiny reset button on the back; well I seem to remember reading somewhere that if you hold that button down longer than say 6 seconds it can wipe out some of the logged settings. So just a thought, but say you had held down the reset a little too long like 8 seconds, that might have messed with some settings. Hopefully someone here with router knowledge can chime in here about that possibility.
Just brain storming.
Just brain storming.